It has been estimated that more than thirteen million Americans suffer from gastroesophageal reflux disease, wherein gastric contents, such as stomach acid, are refluxed into the esophagus. This disease, commonly referred to as GERD, is often associated with an inflammation of the esophagus, known as esophagitis, and can eventually develop into more serious complications known as "Barrett's Esophagus." This development occurs in about ten percent of GERD patients and involves an alteration of the mucosal tissue in the lower esophagus. This alteration involves a transformation from a normal squamous epithelial structure to a columnar form sometimes referred to as specialized intestinal metaplasia, or Barrett's Metaplasia. Further, approximately five percent of Barrett's Esophagus cases subsequently advance to a form of esophageal cancer known as adenocarcinoma. Adenocarcinoma is fatal in about ninety percent of cases.
Various surgical techniques are available to reduce the incidence of reflux, but such procedures are often associated with significant complications. In addition, a number of pharmacological agents, such as protein pump inhibitors (PPI's) are available to reduce the acidity of gastric reflux. Studies have shown that anti-reflux surgery, or treatment with PPI's, can result in a regression of the surface area of Barrett's Metaplasia. However, the only known treatment to completely eliminate the Barrett's Metaplasia is to remove the entire thickness of the afflicted esophageal mucosa. It has been found that following removal of the mucosa, such as by ablation of the tissue, there is a high likelihood that there will be a regrowth of normal epithelial tissue. One way to remove the mucosa is to ablate the tissue by applying various forms of energy to the afflicted tissue. Many presently used ablation techniques, however, have shortcomings.
When tissue ablation techniques are used on tissue in difficult-to-reach locations, such as the lower esophagus, there are at least two significant problems. The first of these involves the difficulty in controlling the depth of the ablation into the tissue. The second involves the difficulty in obtaining uniform ablation over the entire surface area that needs to be ablated. Stated differently, without proper control over how and where the ablation will occur, the result can be "patchy." For example, surgical procedures involving cauterization, laser photoablation, photodynamic therapy, and argon plasma coagulation, all employ well known techniques which require probing the body cavity with an ablating apparatus and then moving the apparatus over the surface area to be ablated. The problem, however, is that surface irregularities, folds into the tissue, and variations in the anatomical configurations of body cavities make each of these techniques somewhat problematical in the uniformity of their ablation. As a result, only a portion of the tissue to be ablated may be destroyed, and in some areas, more tissue may be ablated than was intended. In the case of ablation of Barrett's Metaplasia, by not ablating all of the metaplastic tissue, normal epithelium that regrows over adjacent ablated regions may grow over the unablated region making it difficult to detect an early stage adenocarcinoma.
A technique which has promise in overcoming the shortcomings of the techniques mentioned above is "electrolyte assisted" ablation This form of ablation relies on contacting the tissue to be ablated with an electrolyte, such as a fluid or gel. Electrical energy is applied through the electrolyte to the tissue in contact with the electrolyte. Because the electrical resistance of the electrolyte-tissue interface is significantly high relative to the resistance of the electrolyte itself, most of the energy will be dissipated at this interface in the form of heat, leading to thermal ablation of the superficial tissue at this interface. With electrolyte assisted ablation, the "patchy" problem mentioned above is no longer a concern, since an electrolyte in the form of a liquid or gel will effectively bathe the entire surface area of the tissue that is to be ablated.
Several examples of electrolyte assisted ablation can be given. In each case, however, it should be noted that the device which is used to accomplish the ablation is intended to accommodate a particular anatomy.
U.S. Pat. No. 5,100,388, which issued to Behl et al. for an invention entitled "Method and Device for Thermal Ablation of Hollow Body Organs," discloses a catheter having a conductive material delivery lumen and a distal tip heating element which is suited for hollow body organs, such as the gallbladder. For another type of body cavity, U.S. Pat. No. 5,304,214, which issued to DeFord et al. for a "Transurethral Ablation Catheter," discloses a device that is specifically intended to selectively ablate prostatic tissue about the prostatic urethra. For another, entirely different purpose, U.S. Pat. No. 5,431,649, which issued to Mulier et al. for a "Method and Apparatus for R-F Ablation," discloses a method and device for performing cardiac ablation.
In addition to the various anatomies and body cavities for which specific devices and methods have been disclosed, it is not surprising that the devices themselves vary widely in their structures. For example, U.S. Pat. No. 5,575,788, which issued to Baker et al. for a "Thin Layer Ablation Apparatus," incorporates an expandable member in which the electrolyte is delivered to the ablation site, such as the endometrium, through the expandable member. This is quite different from the Mulier et al. device, mentioned earlier, which delivers a conductive fluid to the ablation site by injection through a hollow, helical electrode. In light of the above, it is understandable that in general, the trend with electrolyte assisted ablation has been toward the development of a specific device and a specific method for use in a specific body cavity.
Regardless which particular body cavity is involved, or what particular device is employed, there are certain factors which need to be considered when performing electrolyte assisted ablation. Specifically, the factors which will impact on the efficacy of the electrolyte assisted ablation include: the extent and nature of the surface area to be ablated; the conductivity of the electrolyte; the power requirements; time; and the temperature at which the tissue will be adequately ablated.
An ability to control any medical device during its operation is always an important consideration. This is particularly so when tissue is being ablated by the device. Accordingly, it is very desirable that, at the very least, there be some capability for "open-loop" control of the device. Preferably, the device can also be operated with "closed-loop" control.
In light of the above, it is an object of the present invention to provide a device, and a method for its use, which is effective for electrolyte assisted ablation of superficial tissue in the esophagus. It is another object of the present invention to provide a device, and a method for its use, which is capable of uniformly ablating a selected surface area of tissue. Yet another object of the present invention is to provide a device which is capable of controlling the depth of tissue ablation over a selected surface area using either open-loop or closed-loop control methods. Still another object of the present invention is to provide a device for performing electrolyte assisted ablation which is operationally simple to use, relatively easy to manufacture, and comparatively cost effective.